Such an apparatus is described in U.S. Pat. No. 2,675,987.
In the known apparatus, the piston must travel some distance before a hydraulic control circuit can be drained thereby causing steam admission to close.
The danger in such an apparatus is that the piston will seize, in which case even though the toggle lever is pushed back towards its tripped position, the toggle lever does not move far enough for the hydraulic circuit to drain, and steam admission is therefore not closed.